LXR linux/arch/arm64/mm/mmap.c

   1/*
   2 * Based on arch/arm/mm/mmap.c
   3 *
   4 * Copyright (C) 2012 ARM Ltd.
   5 *
   6 * This program is free software; you can redistribute it and/or modify
   7 * it under the terms of the GNU General Public License version 2 as
   8 * published by the Free Software Foundation.
   9 *
  10 * This program is distributed in the hope that it will be useful,
  11 * but WITHOUT ANY WARRANTY; without even the implied warranty of
  12 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  13 * GNU General Public License for more details.
  14 *
  15 * You should have received a copy of the GNU General Public License
  16 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
  17 */
  18
  19#include <linux/elf.h>
  20#include <linux/fs.h>
  21#include <linux/mm.h>
  22#include <linux/mman.h>
  23#include <linux/export.h>
  24#include <linux/shm.h>
  25#include <linux/sched.h>
  26#include <linux/io.h>
  27#include <linux/personality.h>
  28#include <linux/random.h>
  29
  30#include <asm/cputype.h>
  31
  32/*
  33 * Leave enough space between the mmap area and the stack to honour ulimit in
  34 * the face of randomisation.
  35 */
  36#define MIN_GAP (SZ_128M + ((STACK_RND_MASK << PAGE_SHIFT) + 1))
  37#define MAX_GAP (STACK_TOP/6*5)
  38
  39static int mmap_is_legacy(void)
  40{
  41        if (current->personality & ADDR_COMPAT_LAYOUT)
  42                return 1;
  43
  44        if (rlimit(RLIMIT_STACK) == RLIM_INFINITY)
  45                return 1;
  46
  47        return sysctl_legacy_va_layout;
  48}
  49
  50/*
  51 * Since get_random_int() returns the same value within a 1 jiffy window, we
  52 * will almost always get the same randomisation for the stack and mmap
  53 * region. This will mean the relative distance between stack and mmap will be
  54 * the same.
  55 *
  56 * To avoid this we can shift the randomness by 1 bit.
  57 */
  58static unsigned long mmap_rnd(void)
  59{
  60        unsigned long rnd = 0;
  61
  62        if (current->flags & PF_RANDOMIZE)
  63                rnd = (long)get_random_int() & (STACK_RND_MASK >> 1);
  64
  65        return rnd << (PAGE_SHIFT + 1);
  66}
  67
  68static unsigned long mmap_base(void)
  69{
  70        unsigned long gap = rlimit(RLIMIT_STACK);
  71
  72        if (gap < MIN_GAP)
  73                gap = MIN_GAP;
  74        else if (gap > MAX_GAP)
  75                gap = MAX_GAP;
  76
  77        return PAGE_ALIGN(STACK_TOP - gap - mmap_rnd());
  78}
  79
  80/*
  81 * This function, called very early during the creation of a new process VM
  82 * image, sets up which VM layout function to use:
  83 */
  84void arch_pick_mmap_layout(struct mm_struct *mm)
  85{
  86        /*
  87         * Fall back to the standard layout if the personality bit is set, or
  88         * if the expected stack growth is unlimited:
  89         */
  90        if (mmap_is_legacy()) {
  91                mm->mmap_base = TASK_UNMAPPED_BASE;
  92                mm->get_unmapped_area = arch_get_unmapped_area;
  93        } else {
  94                mm->mmap_base = mmap_base();
  95                mm->get_unmapped_area = arch_get_unmapped_area_topdown;
  96        }
  97}
  98EXPORT_SYMBOL_GPL(arch_pick_mmap_layout);
  99
 100
 101/*
 102 * You really shouldn't be using read() or write() on /dev/mem.  This might go
 103 * away in the future.
 104 */
 105int valid_phys_addr_range(unsigned long addr, size_t size)
 106{
 107        if (addr < PHYS_OFFSET)
 108                return 0;
 109        if (addr + size > __pa(high_memory - 1) + 1)
 110                return 0;
 111
 112        return 1;
 113}
 114
 115/*
 116 * Do not allow /dev/mem mappings beyond the supported physical range.
 117 */
 118int valid_mmap_phys_addr_range(unsigned long pfn, size_t size)
 119{
 120        return !(((pfn << PAGE_SHIFT) + size) & ~PHYS_MASK);
 121}
 122
 123#ifdef CONFIG_STRICT_DEVMEM
 124
 125#include <linux/ioport.h>
 126
 127/*
 128 * devmem_is_allowed() checks to see if /dev/mem access to a certain address
 129 * is valid. The argument is a physical page number.  We mimic x86 here by
 130 * disallowing access to system RAM as well as device-exclusive MMIO regions.
 131 * This effectively disable read()/write() on /dev/mem.
 132 */
 133int devmem_is_allowed(unsigned long pfn)
 134{
 135        if (iomem_is_exclusive(pfn << PAGE_SHIFT))
 136                return 0;
 137        if (!page_is_ram(pfn))
 138                return 1;
 139        return 0;
 140}
 141
 142#endif
 143